Membrane oxygenators for blood are presently being sold by Travenol Laboratories, Inc., Deerfield, Ill., which contain a microporous, hydrophobic diffusion membrane. The diffusion membrane is pressed between membrane support members, and provided with a pair of flow paths, one for blood along one side of the membrane and another for oxygen and respired gases along the other side of the membrane.
The pores in the hydrophobic material are sufficiently small, compared with the thickness of the material, that blood cannot pass through the membrane. However, the pores provide improved permeability for gases through the membrane. Accordingly, oxygen, carbon dioxide, and water vapor are rapidly exchanged through the membrane. See U.S. Pat. Nos. 3,757,955 and 3,927,980 for descriptions of the construction and use of oxygenators having hydrophobic membranes.
Such oxygenators for blood made of porous, hydrophobic membrane have turned out to be a major step forward in the field of blood oxygenation, and are being used in open heart surgery and other medical procedures with significantly improved success over that which has gone before in the prior art. The devices of this invention exhibit excellent blood compatibility, permitting relatively long-term use, coupled with a high level of blood oxygenation.
However, it has been considered desirable by some experts to use hydrophilic, blood-contacting membranes rather than hydrophobic membranes, for the reason that there is increased compatibility between hydrophilic membranes and the formed elements of the blood, as well as plasma portions, when compared with hydrophobic membranes.
However, hydrophilic membranes may not be rendered porous without causing leakage of aqueous liquids across the membrane, and hydrophilic membranes generally exhibit far less capacity for oxygen and carbon dioxide transfer.
In accordance with this invention, a hydrophobic membrane, preferably a porous, hydrophobic membrane, is provided with a hydrophilic outer surface. Accordingly, the resulting membrane can exhibit the desirable transfer characteristics of hydrophobic membranes, specifically the porous membranes, while at the same time presenting a hydrophilic surface to the blood, resulting in less platelet attachment and the like.
Also, the membranes of this invention, and especially the porous membranes, can be used to process other aqueous liquids in the medical as well as other fields, as well as nonaqueous liquids having surface tensions similar to water, without leakage.